Levothyroxine is a thyroid hormone product, commercially available in 10 different dose strengths. However, only 5 dose strengths are permissible in the present formulary system at NIH. Some clinicians feel that availability of all dose formulations will allow for a safer, more efficacious titration of dose. This randomized control study will evaluate (over a 2-year period) thyroid function, prescribing patterns, patient compliance, frequency of thyroid function studies and clinic visits, medication accuracy, and inventory cost with and without formulary restrictions on levothyroxine dose strengths (5 vs 10 dose strengths). The study population will consist of fifty NIH physicians from the NICHD and NIDDK clinics who prescribe levothyroxine. Results will provide quality assurance and therapeutic drug monitoring information, which can be used to fulfill requirements suggested by the Joint Commission on Accreditation of Hospitals (JCAH).